The present invention relates to electronic devices having a common connector such as a USB (Universal Series Bus) connector which is adapted to connect the device commonly to a plurality peripheral devices.
In digital cameras, the image data obtained by a CCD or like image pickup device is recorded in a memory medium such as DRAM or IC card. When the image output terminal of the camera is connected to a host computer (personal computer), the image data stored in the memory medium can be transferred, for example, to a hard disk drive device.
The digital camera includes as its power source a primary battery or secondary battery, which supplies power for operating circuits when the camera is carried for use. Further digital cameras are known which are settable in a sleep mode (energy saving mode) in which the data processing function is inactivated although the control function is activated in preparation for photo-graphing so as to minimize battery power consumption.
For use as common interface means for connecting a plurality of peripheral devices such as a mouse, keyboard and printer to a personal computer, a USB (Universal Serial Bus) system is used in the field of personal computers in place of interfaces conventionally provided individually for the devices. When the main body of the computer is provided with one USB connector, up to a maximum of 127 peripheral devices can be connected in the form of a star network to the computer body.
Accordingly, investigation is under way on the use of the USB connector for digital cameras for connecting the camera to a host computer by the connector. In this case, it appears useful to realize a hot plug function, such that even when the digital camera is connected in an operating state to the USB connector, the host computer can recognize the digital camera by automatic configuration.
FIG. 3 shows a hot plug-adapted digital camera 10 having a USB connector and a host computer 2 as interconnected by the USB connector. The host computer 2 has four terminals providing the USB connector, i.e., a D+ terminal 21 and Dxe2x88x92 terminal 22 serving as a pair of positive and negative data input-output terminals, a power source output terminal 23 for supplying power to peripheral devices having no power source, and a grounding terminal 24.
On the other hand, the digital camera 10 has a D+ terminal 11 and Dxe2x88x92 terminal 12 to be connected respectively to the D+ terminal 21 and Dxe2x88x92 terminal 22. A pair of positive and negative lines, i.e., a D+ line 41 and Dxe2x88x92 line 42 extending from these terminals 11, 12, are connected to an ASIC (Application Specific Integrated Circuit) 4 for performing various data processing operations. Also connected to the ASIC 4 is a microcomputer 30 for controlling the operation of the ASIC 4 and other circuits.
The digital camera 10 incorporates a power source circuit 5 which comprises a secondary battery and which supplies required power to the microcomputer 30 and the ASIC 4 through a power source line 6. Further connected to the D+ line 41 is a pull-up resistor 8, to which power is supplied also from the power source circuit 5. The digital camera 10, which has the power source incorporated therein, need not be connected to the power source output terminal 23 of the host computer 2 for the supply of power.
When connected to the digital camera 10 by the USB connector, the host computer 2 recognizes the connection by detecting the potential difference xcex94V between the D+ terminal 21 and the Dxe2x88x92 terminal 22, thus realizing a hot plug function.
In the sleep mode, power is supplied to the microcomputer 30, whereas the ASIC 4 is not energized to thereby save the power to be consumed. However, for the host computer 2 to recognize the digital camera 10 when the computer 2 is connected by the USB connector to the camera 10 as set in the sleep mode, the pull-up resistor 8 needs to be held energized at all times. This results in a problem of failing to achieve a sufficient reduction of power consumption owing to the power consumed by the pull-up resistor 8 although the camera 10 is set in the sleep mode.
Another problem encountered is that the digital camera 10 set in the sleep mode is unable to receive data from the host computer 2 because the ASIC 4 is held unenergized in this mode.
Accordingly, an object of the present invention is to provide an electronic device which has diminished power consumption and which is adapted for the hot plug function even in the sleep mode.
The present invention provides an electronic device having a common connector capable of connecting a plurality of peripheral devices commonly to the electronic device and comprising a data processing circuit for performing a specified function by conducting data communication with an information processing device connected to the common connector, a control circuit for controlling the operation of the data processing circuit, means for providing a predetermined potential difference between a pair of positive and negative data lines interconnecting the data processing circuit and the common connector, and a power source circuit for supplying power to the data processing circuit, the control circuit and the potential difference providing means, the electronic device being settable in a sleep mode in which required power is supplied from the power source circuit to the control circuit, and the function of the data processing circuit is partly or entirely inactivated by limiting the supply of power to the data processing circuit.
The electronic device of the invention further comprises a power source input terminal connectable to a power source output terminal provided on the information processing device, means for detecting the connection of the power source output terminal to the power source input terminal, and on/off means for turning on/off the power to be supplied from the power source circuit to the potential difference providing means, the control circuit being operable to hold the on/off means off during a period in which the electronic device is set in the sleep mode, while cancelling the sleep mode and turning on the on/off means upon the connection detecting means detecting the connection.
The potential difference providing means can be provided by a pull-up resistor connected to at least one of the pair of positive and negative data lines interconnecting the data processing circuit and the common connector.
Stated more specifically, the common connector is a USB connector comprising a pair of positive and negative data input-output terminals, and the pull-up resistor is connected to the positive data line which extends from the positive data input-output terminal. The connection detecting means can be provided by connecting the power source input terminal to the control circuit via an inverting circuit.
When the electronic device of the invention is in the sleep mode, the on/off means is held off to prevent the power consumption by the potential difference providing means (pull-up resistor). If the information processing device is connected to the electronic device in this state by the common connector, the connection is detected, for example, by detecting the voltage applied from the power source output terminal on the information processing device to the power source input terminal of the electronic device, and the result of detection is given to the control circuit. The control circuit thereby recognizes the connection of the information processing device to cancel the sleep mode and turn on the on/off means.
Consequently, power is supplied to the potential difference providing means (pull-up resistor), enabling the information processing device to recognize the connection of the electronic device thereto by detecting the potential difference between the pair of positive and negative data lines.
The electronic device equipped with the common connector and embodying the invention attains a greater reduction in power consumption than conventional devices because the potential difference providing means (pull-up resistor) is not energized when the device is in the sleep mode. Further the present device is adapted for the hot plug function because the device, if set in the sleep mode, can be automatically brought out of this mode by the connection of the information processing device.